The metal used is selected or appropriately treated not only to have good bending strength, but above all to have rigidity that is appropriate to its use. Such a collar is put into place by moving the above-specified abutments towards each other by means of a pliers-like clamping tool. This increases the diameter of the collar, thereby making it easily engaged by axial sliding on the hose or other object to be clamped. When the force urging the abutments towards each other ceases to be applied, the energy stored in the collar is released so the collar clamps the hose by attempting to return to its initial diameter.
Consequently, the clamping force of the collar depends on how much its diameter is increased compared with its diameter in the rest state. In addition, given its structure, the collar is capable of deforming elastically to track fluctuations in the diameter of the object to be clamped, and it is thus capable, in theory, of maintaining adequate clamping. This property is particularly important when clamping flexible hoses made of rubber or like materials that are fitted over rigid tubes, whenever it is desired to provide leak-proof connections for ducting that conveys fluids at varying temperatures. Such hoses are known to be liable to creep, so it is therefore desirable for the collar to compensate automatically for any reduction in the diameter of the hose.
The above-mentioned European patent also proposes improving the stiffness of the collar and its bending strength without increasing the thickness of the metal strip. To this end, it provides for reinforcing ribs on the strip that project from the outside surface of the collar and that extend over substantially all of the periphery thereof. However, although that solution is theoretically capable of achieving the desired results, it suffers from the particular drawback of being relatively expensive and sometimes difficult to manufacture, in particular whenever the strip is of any significant thickness.
It will also readily be understood that the clamping pressure exerted by the collar on the periphery of the object to be clamped, in particular a hose that is liable to creep, depends on the bearing area between the collar and the object. In this respect, proposals have already been made, in particular in patent DE-A-3 026 582, to impart a V-shaped section to the strip from which the spring collar is made, in particular for the purpose of increasing the clamping force it provides compared with that of a circular section collar of the same area.
However, collars in accordance with that German patent suffer from the drawback of exceeding the elastic limit of the metal in certain zones of the collar section when the collar is installed On the object to be clamped. As a result, in the event of the diameter of the object to be clamped reducing, e.g. because of creep in a hose, the clamping force of the collar and in particular the clamping pressure on the surface of the object to be clamped runs the risk of being insufficient to ensure that a coupling continues to be leak-proof.
In performing research to improve the efficiency of spring clamps, and in particular of those described in the above-mentioned German patent, while simultaneously seeking a clamp that is as simple and as cheap as possible to manufacture, the Applicant has observed that the angle between the branches of the V-shape of the collar section can be designed so as to avoid any risk of exceeding the elastic limit in certain zones of the collar while it is being put into place. Thus, the general advantages of spring collars as recalled above can be retained even if the diameter of the object to be clamped, and more particularly of hoses involved in leak-proof couplings, varies quite considerably in use.